Of course limonade isn't fizzy, that stuff is called frisdrank.Also I only know it as the sweet fruit-flavoured syrup stuff. There's probably some lemon extract or other acidifier in there to enhance the sweet flavour, but the sweet is always overwhelming.

There is such a thing as drinkable "lemon juice" from concentrate, it's just extremely uncommon. But in the context of ordering lemon juice from a restaurant menu, the name ought to work because you wouldn't expect to receive the stuff used for cooking.